Process in digesting cellulose



March 2, 1937. x s. SVENSSON PROCESS IN DIGESTING CELLULOSE Filed Oct. 3, 1955 J. Svarz 5301 /v YEA/TO)? Patented Mar. 2, 1937 UNITED STATES PATENT OFFICE Application October 3, 1935, Serial No. 43,411 In Sweden October 13, 1934 6 Claims.

In applying the processes for obtaining a circulation of the digesting liquid in digesting cellulose, which processes consist in introducing a gaseous medium by means of an injector, jet

apparatus or other introducing means into a conduit opening at the upper and lower part of the digester, the said conduit being at least at its lower part connected to or provided with a screen element or the like, into which conduit 10 the fibrous material in the digester is prevented from entering, and according to which processes the digesting liquid is caused to circulate from below upwardly in'the conduit and from above downwardly in the space of the digester filled with fibrous material, it has appeared that a rather long time is required to cause a more extensive circulation and to obtain as uniform a temperature of the digesting liquid as possible already at the beginning of the digestion. The inventor has, thus, found that the injector or jet apparatus does not operate completely effectively until the digesting liquid has reached a temperature of about 70 to 80 C. which causes that an unnecessarily long time is required to obtain the desired temperature equalization of the digesting liquid, which at the beginning of the digestion usually has a temperature of about to C. This will also cause that the time necessary for reaching the final digestion tem- 30 perature becomes relatively long.

The said drawbacks are removed by the present invention according to which at least at the beginning of the digesting period the digesting liquid introduced into the digester during the 5 circulation is preheated before it reaches the injector.

The accompanying drawingillustrates a cross section of a sulphite cellulose digester provided with a device for applying the process accord- 40 ing to the present invention.

In the digester l is mounted the circulation conduit 2 the lower part of which being connected to the bottom screen 3 of the digester and the upper part being provided with the screen 4. To the circulation conduit 2 is connected a conduit 5 which is provided with an injector or jet apparatus consisting of the bent pipe 1 and the injector-nozzles 8, through which steam or sulphurous gas or steam and sulphurous gas may be introduced into the circulation conduit. Another steam supply pipe 6 is connected to the circulation conduit 2 at a place situated below the junction with the conduit 5.

55, When the necessary quantity of fibrous material and digesting liquid has been introduced into the digester and the digestion is to begin, steam or sulphurous gas or steam and sulphurous gas first are supplied through the conduit 5, and then steam is supplied to the circulation con- 5 duit through the pipe 6. The quantity of steam supplied through this pipe is preferably adjusted so that the digesting liquid passing through the pipe up to the injector will obtain an increase of temperature, the near to C. the better, 10 since this is the temperature at which the injector begins to operate efiectively. The portion of the tube 6 located in the circulation conduit 2 may be T-formed and provided with perforations, or it may be provided with upwardly l5- directed replaceable nozzles for controlling the steam quantity.

In certain cases it may be suitable to interrupt the steam supply through the tube 6 when the entire digesting liquid has reached the tempera- 20 ture at which the injector operates complete effectively.

Since the injector causes more rapid circulation when the digesting liquid is preheated the advantage is obtained that considerably large 25 heat quantities may be supplied for a short period so that the starting period and consequently also the digesting period become shorter. This is obtained according to the invention without using any expensive devices for preheating the digest- 30 ing liquid prior to the same being supplied to the digester.

The steam supply pipe 6 need not be connected to the circulation conduit 2. It may also open into the bottom of the digester in the vicinity of, 35 or at the screen 3 since, due to the action of the injector or the jet apparatus, the liquid surrounding the screen 3 is sucked into the circulation conduit and it is, of course, just the liquid surrounding the screen which is heated when 40 steam is introduced into the bottom of the digester.

The distance between the conduits 5 and 6 at the places where they open into the circulation conduit should be so great that the heat supplied will be uniformly distributed before the order to cause a circulation of the digesting liquid from below upwardly in the conduit and from above downwardly through the space of the digester filled with fibrous material, and into which conduit the fibrous material is prevented from entering, the conduit being at least at the lower part connected to a screen element, preheating the digesting liquid on its way upwards before it reaches the injector, at least at the beginning of the digesting period.

2. In a process as claimed in claim 1, introducing steam as gaseous medium into the conduit.

3. In a process as claimed in claim 1, introduc- 

